1. Field of the Invention
The present invention concerns improving the cleaning properties of organic solvents used in dry cleaning operations, and especially, concerns improving the cleaning properties of such organic dry cleaning solvents by removing residual moisture therefrom as well as sulfur and other residual reducing agents by the oxidation of the same. More specifically, the present invention relates to an improved dry cleaning operation as compared to my prior U.S. Pat. No. 3,766,075 issued on Oct. 16, 1975.
2. Description of the Prior Art
In commercial dry cleaning operations, various types of organic solvents have been employed in the past in the dry cleaning process to remove soils from fabrics and clothing. For example, the prior art has employed solvents such as halogen-substituted aliphatic hydrocarbons such as perchloroethylene (tetrachloroethylene), mineral spirits, various types of petroleum solvents, mixtures of hydrocarbon and halogen-substituted hydrocarbon solvents with detergents, and the like. Typically, the solvents employed in dry cleaning operations have a boiling point in the range of from about 100.degree. to about 400.degree. F and a surface tension of from about 20 to about 30 dynes/cm at room temperature (i.e., 20.degree. C) as measured against an air interface. A typical prior art formulation of a halogenated hydro-carbon solvent-detergent combination is manufactured by DuPont and sold under the trade name Valclene, which is a combination of a fluorocarbon solvent and a special high-performance detergent with a boiling point of about 118.degree. F, a density of about 13.16 pounds per gallon at 68.degree. F and a surface tension at 68.degree. F of about 20 dynes/cm. A suitable fluorocarbon solvent is trichlorotrifluoroethane as the solvent constituent for Valclene.
Other solvents such as carbon tetrachloride and methylisobutylketone have also been employed in the past in commercial dry cleaning operations. Due to the good stability and relatively high cost of these solvents, they are naturally reused and continuously recycled in the dry cleaning process, and thus it becomes desirable to recondition the solvents by removing residual moisture, sulfur, and other residual reducing agents therefrom in order to provide reconditioned solvent for cleaning successive batches of soiled fabrics and clothing.
The prior art, in an effort to remove such impurities from dry cleaning solvents, suggests that the formulations used as the solvents be distilled after the drying cleaning operation; however, distillation is normally expensive and sometimes difficult to conduct without costly equipment, and problems arise in some instances because of the loose additives present in the dry cleaning mixtures.
Another suggested solution for the removal of the impurities from the solvents is by a filtration and absorption technique wherein the impurities are selectively removed from the solvents after the same have been used to clean soiled fabrics. However, the use of such techniques is disadvantageous in that equipment cost becomes high, and other mechanical problems with respect to the apparatus prevent this method from being efficiently conducted. In addition, the loose additives which may be present in the dry cleaning formulation may tend to inhibit effective filtration and absorption.
The prior art also suggests the addition of water to common formulations of dry cleaning mixtures in order to improve the dry cleaning characteristics of the solvents employed for the cleaning operations. Normally, water would be added to dry cleaning solvents to enable the solvents to dissolve water-soluble components of stains on fabrics or clothing. However, most modern fabrics are non-wettable and the presence of water, even in small amounts, prevents the organic solvents, which are generally non-polar in nature, from dissolving slightly polar stains such as fats, etc., in the solvents since the stains become hydrated through dipole-dipole bonding with the water molecules.
During the dry cleaning operation, the relative humidity of the solvent changes according to the humidity of the ambient air and that present in the fabric or clothing being cleaned. Normally, the relative humidity of the solvents is maintained at about 65 to 70% in order to dissolve, for example, salts and sugars from stains. However, the control of the amount of moisture which is present in organic dry cleaning solvents is very important, since serious problems are encountered if the amount of moisture in the solvents becomes eiter too high or too low.
Too much moisture in dry cleaning solvents may result in fiber shrinkage or distortion, the dulling of colors of the fabrics or clothing being cleaned and possible fading of the fabrics. In addition, fabrics become harder to press following cleaning. Too low a moisture level in the solvent results in the redepositing of water-soluble substances on the fabrics or clothing being cleaned, with the result that stains cannot be effectively removed. Further, a low moisture content in the dry cleaning solvent may result in carbon being redeposited on the fabric, thereby adversely affecting the color of the fabric and leaving the fabric with static electricity charges which make it uncomfortable for a person to subsequently wear the clothing; in addition, the presence of static electricity charges present a danger of explosion with certain types of solvents.
In addition to the problems inherent in the use of dry cleaning solvents containing too much or too little moisture, other problems are apparent due to the presence of impurities such as sulfur and other reducing agents in dry cleaning solvents. Such impurities may deposit on the fibers of the clothing being cleaned, resulting in discoloration and spotting thereof, or their presence in the solvents may result in fading of the colors of the fabrics being cleaned, may cause odors to remain on the cleaned products, and in addition, especially with respect to sulfur impurities, may cause corrosion of the equipment being used to clean the material.
In my prior Pat. No. U.S. 3,766,075, on invention was disclosed wherein residual moisture and impurities contained in typical formulations of dry cleaning solvents could be removed (without creating the adverse effects known to the prior art) by adding an unsubstituted aromatic hydrocarbon or a halogen or alkyl-substituted aromatic hydrocarbon together with a dried cellulosic material onto which has been precipitated a fine deposit of an oxidizing agent such as lead dichromate to an organic dry cleaning solvent. The treated cellulosic material was disclosed as absorbing excess moisture present in the solvent mixture as well as removing impurities therefrom through oxidation by means of the employed dichromate.
The present invention is an improvement on the preceeding dry cleaning composition and method.
Accordingly, it is a principal object of the present invention to provide a means of removing residual moisture from typical formulations of dry cleaning solvents.
It is a further object of the present invention to provide improved dry cleaning compositions free of residual moisture and impurities, without the adverse effects shown in the prior art.
It is a further object of the present invention to provide a method of removing impurities contained in the solvents as a result of the dry cleaning operation.
It is a further object of the present invention to provide a method of dry cleaning using such improved dry cleaning solvents.
It is a further object of the present invention to provide a cellulosic container device which can be employed in dry cleaning solvents to improve the dry cleaning operation.
Other objects and advantages of the present invention will become apparent from the ensuring description.